80 MOSQUITOES OF NORTH AMERICA 
among the salivary glands and other viscera. Other smaller masses lie in the 
head and abdomen.” 
THE TRACHEAL SYSTEM. 
There are two main tracheal trunks, passing along each side of the body near 
the digestive canal. A branch is sent off to each spiracle and other branches pass 
to the different organs and ramify through the body. The thoracic spiracles 
are described on another page in connection with their function in the produc- 
tion of sound. Both spiracles and trachee of the thorax are greatly developed. 
The abdominal spiracles are very small and the tracheal trunks are much more 
slender in this part of the body than in the thoracic region. No large air-sacs 
belonging to the tracheal system are present. The branches of the tracheal 
system are described by Christophers as follows: 
“ The Trachee.—Very large trachee pass inwards from the anterior thoracic 
spiracles. 
“1. A large branch passes forwards towards the neck and gives off a branch 
which passes down on either side of the middle line to the two anterior coxe and 
the salivary glands. The main branch continues on through the neck, and sup- 
plies the head with numerous large branches. 
“2. A large branch passes upwards and backwards along the edge of the meso- 
scutum, and gives off branches which supply the wing muscles. A smaller 
branch also passes forwards and supplies the muscles of the thorax. 
“3. The largest trachea in the body (main trachea) passes downwards, back- 
wards, and inwards, so as to lie on either side of the anterior portion of the 
alimentary canal. Numerous branches are given off from this trunk to the 
thoracic muscles, the alimentary canal, and legs. Posteriorly the trunk is con- 
tinuous with a trachea passing forwards from the second thoracic spiracle, thus 
forming on either side a large tracheal loop. 
“ Large trachee also pass inwards from the posterior thoracic spiracles. 
“1. Branches pass forwards and join in a loop with the main trachea, also 
backwards to join the abdominal system. 
“2. Branches pass downwards to the meta-thorax and posterior pair of legs. 
“ 3, Branches pass inwards to the muscles and mid-gut. 
“From each abdominal spiracle a short thick trunk passes inwards which 
gives rise to the following branches :— 
“ A dorsal branch ramifying beneath the tergum and joining the branch of the 
opposite side. 
“ A sternal branch supplying the sternal plate and muscles, also joining the 
branch of the other side. 
“ Loop branches passing to the trunks anterior and posterior. 
“ Branches passing inwards and supplying viscera. Branches from the first, 
second, third, and fourth abdominal trachee supply mainly the mid-gut, those 
from the fourth and fifth the ovaries, those from the sixth and seventh the 
genital organs.” 
* HISTOLOGY. 
“THE ALIMENTARY CANAL AND APPENDAGES. 
“The epithelial lining differs considerably in the mid-gut from either the 
fore-gut or hind-gut. In the mid-gut the possession of a marked striated border 
by the epithelial cells is characteristic. The muscular fibres of the alimentary 
canal are striated throughout. 
“ The Fore-gut.—The anterior portion of the fore-gut is lined by chitin and 
does not differ from the cuticle in structure. It consists of a single layer of 
cubical cells of small size. The esophageal dilatation and its diverticula re- 
